Today, out of concern for the environment, there is a demand for the percentage occupied by natural energy to be increased.
However, natural energy is easily affected by weather changes. If wind power and solar power generation increases, the amount of power generated will increase or decrease depending on the weather. If the total amount of power generated and the total amount of power consumed are out of balance, the frequency of the electric power system fluctuates. If the frequency fluctuates, a disturbance will occur in the electric power system. In order to balance the total amount of power generated and the total amount of power consumed, there are methods of adjusting power supply, such as, for example, storing surplus power in a rechargeable battery and, when the amount of power generated is insufficient, using the power stored in the rechargeable battery to make up for the insufficient power. However, rechargeable batteries are still expensive, and deploying rechargeable batteries sufficient for adjustment is difficult. Thus, methods of adjusting power demand have been proposed. For example, in JP-A No. 2006-353079, there is proposed an electric power system stabilization system that controls, via a communication line, the power consumption of a plurality of specific loads connected to an electric power system to thereby balance the time series total amount of generated power and the time series total amount of consumed power and stabilize the frequency of the electric power system.